Magnetic cortical oscillations associated with subjective auditory coolness during paired comparison of time-varying HVAC sounds.

The impressions of heating, ventilation, and air conditioning (HVAC) sounds are important for the comfort people experience in their living spaces. Revealing neural substrates of the impressions induced by HVAC sounds can help to develop neurophysiological indices of the comfort of HVAC sounds. There have been numerous studies on the brain activities associated with the pleasantness of sounds, but few on the brain activities associated with the thermal impressions of HVAC sounds. Seven time-varying HVAC sounds were synthesized as stimuli using amplitude modulation. Six participants took part in subjective evaluation tests and MEG measurements. Subjective coolness of the HVAC sounds was measured using the paired comparison method. Magnetoencephalographic (MEG) measurements were carried out while participants listened to and compared the time-varying HVAC sounds. Time-frequency analysis and cluster-based analysis were performed on the MEG data. The subjective evaluation tests showed that the subjective coolness of the amplitude-modulated HVAC sounds was affected by the modulation frequency, and that there was individual difference in subjective coolness. A cluster-based analysis of the MEG data revealed that the brain activities of two participants significantly differed when they listened to cooler or less cool HVAC sounds. The frontal low-theta (4-5 Hz) and the temporal alpha (8-13 Hz) activities were observed. The frontal low-theta and the temporal alpha activities may be associated with the coolness of HVAC sound. This result suggests that the comfort level of HVAC sound can be evaluated and individually designed using neurophysiological measurements.